Clean up the build framework for pcc
- use <bsd.init.mk> to include <../Makefile.inc> files
- add Makefile.inc files that pull in appropriate build settings
- fix the LIBEXECDIR definition (should have trailing /)
- make cc.1 install as pcc.1 to match the binary
- use YHEADER= to build the yacc headers
- general consistency tidy up